I. Field of the Invention
This invention relates generally to implantable medical devices of the type including a pulse generator for stimulating tissue structures via medical leads and more particularly to a device for monitoring the force applied to a proximal terminal of the medical lead by a lead terminal lock mechanism in the implantable device.
II. Discussion of the Prior Art
Implantable medical devices, such as cardiac rhythm management devices and neural stimulators typically comprise a pulse generator contained within a hermetically sealed housing and which provides electrical stimulating pulses to target tissue through a medical lead. The medical lead comprises an elongated flexible plastic lead body having one or more electrodes at a distal end thereof and a terminal pin at a proximal end. The proximal terminal may include one or more electrical contacts that are insulated from one another and connected by elongated conductors extending through the lead body and connected to the distal electrodes.
Affixed to the housing of the pulse generator is a header, typically formed from an insulating plastic, and having a longitudinally extending bore into which the proximal terminal of the medical lead may be inserted. Disposed in the longitudinal bore are one or more contacts for mating with the contact on the lead's proximal terminal. The header contacts are connected by feed through wires, which extend through hermetic seals into the interior of the housing where they connect to the electronic circuitry comprising the pulse generator.
To prevent the lead's proximal terminal from moving within the lead receiving bore of the header, a lead lock is generally provided. One form of lead lock typically comprises a metal or plastic block captured in the lead receiving bore of the header, where the block includes a bore coaxially aligned with the lead receiving bore in the header. A transverse threaded bore is formed that intersects with the longitudinal bore in the block. A setscrew is fitted into the threaded bore and is intended to be tightened against a proximal end portion of the medical lead's terminal pin when inserted into the header to thereby prevent longitudinally directed forces on the lead from pulling the terminal pin free from the pulse generator's header.
It may happen, however, that an implanting physician may fail to adequately advance the setscrew with a sufficient force to hold the lead terminal in place. Such an event can result in a failure of the tissue stimulating device to properly function and, of course, is to be avoided.
A need, therefore, exists for a way of indicating whether a lead lock mechanism in the header of an implantable tissue stimulating device has been engaged so as to positively lock the proximal terminal of a medical lead in place. The present invention meets that need.